1. Field of the Invention
The present invention relates to techniques of a control network system, a master apparatus, a control data processing method, and a control data processing program.
2. Description of the Related Art
In a configuration of a control system, one or more control computers (master apparatuses) control one or more controlled devices (slave devices) via a network. The master apparatus controls the slave device by transmitting a control packet including a control instruction or the like to the slave device. The network in which the control packet flows is, for example, DeviceNet, CC-Link (registered trademark), and EtherCAT (registered trademark).
An API (Application Programming Interface) in a control application includes various methods. In one of the methods, a packet to be transmitted is built in the API itself, and a control instruction is stored in a data area in the packet.
In another method of the API, a data area of a controlled object is allocated to an address space to which is accessible from a control application, and a control instruction is written to the data area. The control instruction written to the address space is built as an outgoing packet using a prescribed technique and is transmitted to a network.
In some cases, the address space is a software object developed in a memory. In others, the address space is a bus space in a hardware which is accessible from a computation unit such as a CPU.
One of methods of allocating a data area to a prescribed address space is a transfer memory method (see Japanese Laid-Open Patent Application, Publication No. 2000-076163, and ISO (International Organization for Standardization) 14745-4, “Industrial Automation Systems and integration-Open systems application integration frameworks, Part 4 Reference description for Ethernet-based control systems”. In the transfer memory method, data areas of all nodes constituting a network are allocated to an address space in equal size. Data in the address spaces in the all nodes are periodically exchanged among the all nodes via communications. Networks using the above-mentioned method include CC-Link and FL-net. The transfer memory method is also called a common memory method.
Another method of allocating a data area to a prescribed address space is a logical address space method. In the logical address space method, a given data area owned by each slave is allocated to a single virtual logical address space. Size of the allocated area or how to allocate can be arbitrarily set. Networks using the method as described above include EtherCAT (registered trademark) (see IEC61784, Part 2, Communication Profile Family 12).
With regard to an API in a method communicating a control instruction to a controlled object, a conventional technology has a difficulty in solving problems such as efficiency of developing software, communication performance in software, flexibility of network configuration, or the like.
In the method in which an outgoing packet is generated in an application and a control instruction to a controlled object is stored in the outgoing packet, an application developer is required to understand a communications protocol of a network. However, in developing such a control application, the application developer preferably focuses on realization of a desired control method and achievement of a target control performance. If the application developer has to understand details of a communications protocol, development man-hours are increased and application development becomes complicated, which is disadvantageous.
Further, if communications software such as an operating system (to be abbreviated as an OS hereinafter) is used, communication processing time is increased, and control performance in an entire system is decreased. Such communications software includes, for example, a TCP/IP protocol stack (which is described hereinafter as a protocol stack of communications software). A communication processing using a protocol stack requires an increased communication processing time because a control application and a communication processing are sequentially executed. Moreover, if other application is running on the OS, a runtime thereof also affects and may further increase the communication processing time.
In the transfer memory method, a data area of a controlled object is allocated into an address space, and an instruction is read or written to the data area. The method has an advantage that there is no need of understanding details of a communications protocol, compared to a method of generating an outgoing packet inside an application. However, in the transfer memory method, because data areas in fixed size as many as all nodes are allocated to an address space, the number of nodes connectable to the network tends to be limited.
The fixed-sized data area tends to create an unused free space therein. For example, assume a case where there are two controlled objects. One has scores of I/O of “2”, and the other, “1,000”. If a size of a target data area has “1,024”, the latter controlled object can efficiently utilize the data area, but the former cannot, leaving almost all of the data area meaningless.
In the logical address space method, a data area of a controlled object can be arranged with less limitations, as compared to the transfer memory method. The logical address space method thus has a high use efficiency of an address space and smaller limitations on the number of connectable nodes. A network using the logical address space method has a larger maximum allowable number of connectable nodes than that of a network using the transfer memory method.
The logical address space method, however, also requires the developer to well understand which meaning a data at a prescribed address location has in an application, similarly to the transfer memory method. Therefore, it is not possible to develop an application in such a way that a meaning in a control application is expressed. The developer executes a processing on the application, to a prescribed address, which decreases development efficiency.
The logical address space method requires the application developer to have expertise on a logical address space or a network (such as generation of an outgoing packet), which results in prolonged time of application development and thus, further sophisticated necessary skills. This also increases cost of application development. Additionally, implementation by software requires sequential execution, which results in a prolonged communication processing time and deterioration of control performance.
The present invention has been made in an attempt to solve the above problems and provide an information processing apparatus having improved development efficiency and communication performance.